1. Field of the Invention
The present invention relates to novel cure accelerators that can be useful for anaerobic curable compositions, such as adhesives and sealants.
2. Brief Description of Related Technology
Anaerobic adhesive compositions generally are well-known. See e.g. R. D. Rich, “Anaerobic Adhesives” in Handbook of Adhesive Technology 29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.
Conventional anaerobic adhesives ordinarily include a free-radically polymerizable acrylate ester monomer, together with a peroxy initiator and an inhibitor component. Often, such anaerobic adhesive compositions also contain accelerator components to increase the speed with which the composition cures.
Desirable anaerobic cure-inducing compositions to induce and accelerate cure may include one or more of saccharin, toluidines, such as N,N-diethyl-p-toluidine (“DE-p-T”) and N,N-dimethyl-o-toluidine (“DM-o-T”), acetyl phenylhydrazine (“APH”), maleic acid, and quinones, such as napthaquinone and anthraquinone. See, e.g., U.S. Pat. No. 3,218,305 (Krieble), U.S. Pat. No 4,180,640 (Melody), U.S. Pat. No 4,287,330 (Rich) and U.S. Pat. No 4,321,349 (Rich).
Saccharin and APH are used as standard cure accelerator components in anaerobic adhesive cure systems. The LOCTITE-brand anaerobic adhesive products currently available from Henkel Corporation use either saccharin alone or both saccharin and APH in most of its anaerobic adhesives. These components however have come under regulatory scrutiny in certain parts of the world, and thus efforts have been undertaken to identify candidates as replacements.
Examples of other curatives for anaerobic adhesives include thiocaprolactam (e.g., U.S. Pat. No. 5,411,988) and thioureas [e.g. U.S. Pat. No. 3,970,505 (Hauser) (tetramethyl thiourea), German Patent Document Nos. DE 1 817 989 (alkyl thioureas and N,N′-dicyclohexyl thiourea) and 2 806 701 (ethylene thiourea), and Japanese Patent Document No. JP 07-308,757 (acyl, alkyl, alkylidene, alkylene and alkyl thioureas)], certain of the latter of which had been used commercially up until about twenty years ago.
Loctite (R&D) Ltd. discovered a new class of materials—trithiadiaza pentatlenes—effective as curatives for anaerobic adhesive compositions. The addition of these materials into anaerobic adhesives as a replacement for conventional curatives (such as APH) surprisingly provides at least comparable cure speeds and physical properties for the reaction products formed therefrom. See U.S. Pat. No. 6,583,289 (McArdle).
U.S. Pat. No. 6,835,762 (Klemarczyk) provides an anaerobic curable composition based on a (meth)acrylate component with an anaerobic cure-inducing composition substantially free of acetyl phenylhydrazine and maleic acid and an anaerobic cure accelerator compound having the linkage —C(═O)—NH—NH— and an organic acid group on the same molecule, provided the anaerobic cure accelerator compound excludes 1-(2-carboxyacryloyl)-2-phenylhydrazine. The anaerobic cure accelerator is embraced by:
where R1-R7 are each independently selected from hydrogen and C1-4; Z is a carbon-carbon single bond or carbon-carbon double bond; q is 0 or 1; and p is an integer between 1 and 5, examples of which are 3-carboxyacryloyl phenylhydrazine, methyl-3-carboxyacryloyl phenylhydrazine, 3-carboxypropanoyl phenylhydrazine, and methylene-3-carboxypropanoyl phenylhydrazine.
U.S. Pat. No. 6,897,277 (Klemarczyk) provides an anaerobic curable composition based on a (meth)acrylate component with an anaerobic cure-inducing composition substantially free of saccharin and an anaerobic cure accelerator compound within the following structure
where R is selected from hydrogen, halogen, alkyl, alkenyl, hydroxyalkyl, hydroxyalkenyl, carboxyl, and sulfonato, and R1 is selected from hydrogen, alkyl, alkenyl, hydroxyalkyl, hydroxyalkenyl, and aralkyl, an example of which is phenyl and N-methyl phenyl glycine.
U.S. Pat. No. 6,958,368 (Messana) provides an anaerobic curable composition. This composition is based on a (meth)acrylate component with an anaerobic cure-inducing composition substantially free of saccharin and within the following structure
where Y is an aromatic ring, optionally substituted at up to five positions by C1-6 alkyl or alkoxy, or halo groups; A is C═O, S═O or O═S═O; X is NH, O or S and Z is an aromatic ring, optionally substituted at up to five positions by C1-6 alkyl or alkoxy, or halo groups, or Y and Z taken together may join to the same aromatic ring or aromatic ring system, provided that when X is NH, o-benzoic sulfimide is excluded from the structure. Examples of the anaerobic cure accelerator compound embraced by the structure above include 2-sulfobenzoic acid cyclic anhydride, and 3H-1,2-benzodithiol-3-one-1,1-dioxide.
Notwithstanding the state of the art, there is an on-going desire to find alternative technologies for anaerobic cure accelerators to differentiate existing products and provide supply assurances in the event of shortages or cessation of supply of raw materials. Moreover, since certain of the raw materials used in the anaerobic cure inducing composition have to one degree or another come under regulatory scrutiny, alternative components would be desirable. Accordingly, it would be desirable to identify new materials that function as cure components in the cure of anaerobically curable compositions.